Hot gases produced via combustion within a gas turbine engine are directed into a turbine. Energy present in the hot gases is used to turn rows of turbine blades and this generates electrical energy and turns the upstream compressor rotor. In order to increase an efficiency of this energy extraction, rows of turbine vanes are disposed between each of the rows of turbine blades. The turbine vanes within each of these rows properly orient the hot gases passing there through for optimal interaction with the next row of turbine blades.
The turbine blades may be disposed on a central rotor shaft because they turn with the rotor shaft. In contrast, the turbine vanes, which must remain stationary, must be mounted another way. In certain configurations the turbine vanes are mounted on an inner perimeter of a turbine vane carrier ring. The turbine vane carrier ring may, in turn, be mounted to the engine casing. The logistics of assembly and disassembly of the gas turbine engine could permit a one-piece turbine vane carrier. However, for sake of simplicity of maintenance etc. in current practice a two-piece turbine vane carrier is often used. When using the two-piece vane carrier ring, an upper half and a lower have are often joined together by bolting together flanged-ends of each half.
During startup, regular operation, and shutdown, temperatures within the gas turbine engine may vary from steady state operating conditions. These instances are known as transients. Associated with a change in temperature may be a change in dimensions of the component. However, the dimensional changes may not be uniform throughout a volume of the component, resulting in a distortion of a shape of the component during the transients. This phenomenon may control permissible tolerances between parts having relatively different thermal responses. One result is that tolerances might be made larger than would be optimal during steady state conditions so that during transient temperature conditions any thermal growth mismatch will not result in the components interfering with (growing into) each other. For example, a gap between tips of rotating turbine blades and a respective sealing surface, which is disposed on an inner perimeter of ring segments surrounding the turbine blades, must be sized to minimize contact (rubbing) between the tip and the sealing surface and associated blade tip material loss related to thermal growth mismatch. However, this reduces engine performance.
In certain configurations the turbine vane carrier also holds the ring segments. However, the turbine vane carrier and associated structure may have a different thermal response than the turbine blades and associated structure. As a result, the turbine vane carrier must be thermally regulated to control a gap between the tips of the rotating blades and the blade sealing surface. Conventional thermal regulation is known to draw compressed air from the compressor and direct the compressed air to a plenum surrounding the turbine vane carrier. During base load operation this compressed air generally cools the turbine vane carrier, and then passes through the turbine vane carrier and into bases of the turbine vanes, where it cools the turbine vanes prior to exiting into a hot gas path within the turbine.